This invention relates to a process for the production of spherical porous fillers for liquid chromatography.
The filler of this invention is porous and it can perform molecular size separation. Accordingly, it is suitable for gel permeation chromatography (hereinafter referred to as "GPC"). Further, a product obtained by introducing ion exchange groups into this filler is a column filler suitable for ion exchange chromatography of substances dissociable in water, such as amino acids, substances related to nucleic acids and proteins. The filler having ion exchange groups introduced therein is specificaly a cation exchanger of the sulfonate type.
Ion exchangers of the so-called standard type or gel type prepared according to the conventional methods such as disclosed in U.S. Pat. Nos. 2,366,007, 2,591,573 and 2,614,099 and Japanese Patent Publications No. 2239/57 and No. 10343/63 have generally a cross-linking agent content of about 1 to about 16%. Ion exchangers having a cross-linking agent content of 1 to 10% are relatively soft and when an eluent is passed at a high flow rate, the loss in column pressure is extreme. Accordingly, if a rapid analysis is conducted by using such soft ion exchangers, it often happens that a pressure exceeding the pressure limit of an analyzing device is applied. Therefore, use of such soft ion exchangers is not suitable for a rapid analysis. On the other hand, when the cross-linking agent content is elevated beyond 10% so as to harden ion exchangers, the rate of the ion exchange reaction is drastically lowered so that it is impossible to accomplish a rapid analysis. Therefore, these ion exchangers are not suitable as fillers for liquid chromatography.
As ion exchangers capable of overcoming these disadvantages, a porous, particulate ion exchanger prepared according to a process disclosed in Japanese Pat. No. 307,263 or Japanese Patent Publication No. 14739/71 is known. On the other hand, in order to obtain a filler having a high activity, the size distribution in the particulate filler must be narrowed. In general, however, it is impossible to obtain a filler having a narrow size distribution according to polymerization alone. Therefore, a particle size classification is generally performed by hydraulic classification utilizing the principle that the sedimentation speed differs depending on the particle size. In fillers obtained by using a precipitant, for example, as disclosed in Japanese Pat. No. 307,263, since the specific gravity of the obtained filler particles is not constant but is different depending on the particle size, with this hydraulic classification it is impossible to obtain a product having a narrowed size distribution. Moreover, according to the process of Japanese Pat. No. 307,263, the precipitation state of polymers is not constant so that it is impossible to obtain a porous polymer having uniform porosity and particle size. Therefore, if a molecular size separation is conducted with use of a polymer such as prepared according to the above Japanese Pat. No. 307,263 the peak width is broadened and the separation accuracy is very low. Thus, porous particles prepared with use of a precipitant are not suitable as fillers for liquid chromatography.
According to the process of Japanese Patent Publication No. 14739/71, as is apparent from the Examples thereof a high molecular weight polystyrene is dissolved in a monomer mixture of styrene and divinyl benzene and a relatively large amount of toluene is added to the resulting oil phase to reduce the viscosity thereof. Even if toluene is added, the viscosity of the oil phase is still high and therefore, it is very difficult to obtain a particulate copolymer of a fine particle size suitable for the above-mentioned use. Moreover, it is relatively difficult to remove the high molecular weight polystyrene from such particulate copolymer.